Chapter 4
Propagation, Antennas, and
Feed Lines
Propagation
 Radio waves travel outward from an
antenna in a straight line
 3 phenomena possible after that:
 Reflection
 Bouncing wave off reflective surface
 Refraction
 Gradual bending of wave while traveling
through atmosphere
 Diffraction
 Redirection of wave around edge of solid
object
Propagation
 Line-of-sight (LOS)
 Direct from transmitting antenna to receiving
antenna
 Radio horizon
 Point at which radio signals are blocked by curvature
of the earth
 Slightly greater than visual horizon
 Refraction increases radio horizon distance by
about 15%
Propagation
 Diffraction: Redirection of wave around edge
of solid object
 Knife edge diffraction
Propagation
 Multi-path
 Transmitted radio waves reflected off various
objects will arrive at receive antenna at different
times
 Result: “Picket fencing”
Propagation
 Radio waves can pass through openings in solid
objects
 Longest dimension of opening at least ½
wavelength
 Because of shorter wavelength, UHF signals can pass
through building openings better than VHF signals
Propagation
 Tropospheric Ducting
 Radio waves can travel for long distances along
vertical boundaries of different temperature air
layers
 Propagation of 300 miles or more possible on VHF
or UHF
T3A01 -- What should you do if another operator
reports that your station’s 2 meter signals were strong
just a moment ago, but now they are weak or
distorted?
A. Change the batteries in your radio to a different
type
B. Turn on the CTCSS tone
C. Ask the other operator to adjust his squelch
control
D. Try moving a few feet or changing the direction
of your antenna if possible, as reflections may be
causing multi-path distortion
T3A02 -- Why are UHF signals often more
effective from inside buildings than VHF signals?
A. VHF signals lose power faster over distance
B. The shorter wavelength allows them to more
easily penetrate the structure of buildings
C. This is incorrect; VHF works better than UHF
inside buildings
D. UHF antennas are more efficient than VHF
antennas
T3A06 -- What term is commonly used to
describe the rapid fluttering sound sometimes
heard from mobile stations that are moving
while transmitting?
A. Flip-flopping
B. Picket fencing
C. Frequency shifting
D. Pulsing
T3A08 -- Which of the following is a likely cause
of irregular fading of signals received by
ionospheric reflection?
A. Frequency shift due to Faraday rotation
B. Interference from thunderstorms
C. Random combining of signals arriving via
different paths
D. Intermodulation distortion
T3C05 -- Which of the following effects might
cause radio signals to be heard despite
obstructions between the transmitting and
receiving stations?
A. Knife-edge diffraction
B. Faraday rotation
C. Quantum tunneling
D. Doppler shift
T3C06 -- What mode is responsible for allowing
over-the-horizon VHF and UHF communications
to ranges of approximately 300 miles on a
regular basis?
A. Tropospheric scatter
B. D layer refraction
C. F2 layer refraction
D. Faraday rotation
T3C08 -- What causes tropospheric ducting?
A. Discharges of lightning during electrical storms
B. Sunspots and solar flares
C. Updrafts from hurricanes and tornadoes
D. Temperature inversions in the atmosphere
T3C10 -- What is the radio horizon?
A. The distance over which two stations can
communicate by direct path
B. The distance from the ground to a
horizontally mounted antenna
C. The farthest point you can see when
standing at the base of your antenna tower
D. The shortest distance between two points
on the Earth's surface
T3C11 -- Why do VHF and UHF radio signals
usually travel somewhat farther than the visual
line of sight distance between two stations?
A. Radio signals move somewhat faster than
the speed of light
B. Radio waves are not blocked by dust
particles
C. The Earth seems less curved to radio waves
than to light
D. Radio waves are blocked by dust particles
Propagation
 Ionosphere
 The upper layers of
the atmosphere are
ionized by UV
radiation from the
sun
 30 to 260 miles above
the Earth’s surface
Propagation
 Ionosphere
 The ionosphere is
divided into layers or
regions
 Each layer has unique
characteristics
Propagation
 Ionosphere
 Transmissions in some radio frequency bands
(e.g., HF & lower VHF) will be reflected off the
ionosphere and return to earth
 Called “skip”
 Skip distances are well beyond the range of line-ofsight
 Several hundred to several thousand miles
• Maximum of about 2500 miles for a single hop
• Can have multiple hops
Propagation
 Ionosphere
 The higher the amount of ionization, the better
radio waves are refracted by the ionosphere
 Amount of ionization varies with time of day
 Sunrise to sunset  higher ionization level
 Amount of ionization varies with sunspot activity
 More sunspots  higher ionization level
 Larger sunspots  higher ionization level
 Number and size of sunspots varies over an 11-year cycle
 Currently in declining portion of Cycle 24
Propagation
 Ionosphere
Propagation
 Ionosphere
 Skip is refraction (bending), not reflection
(bouncing)
 The shorter the wavelength (higher frequency), the less
the signal is refracted (bent).
 At some given frequency, the wave is no longer bent
enough to return to earth
 Known as the “critical frequency”
 Skip normally occurs in the F-layer (F1 & F2)
 Can occur in the E-layer
Propagation
 Ionosphere
 The highest frequency that can be used to
communicate between 2 points is called the
Maximum Useable Frequency (MUF)
 The lowest frequency that can be used to
communicate between 2 points is called the
Lowest Useable Frequency (LUF)
 MUF & LUF vary over any 24-hour period
depending on the amount of ionization in the
ionosphere
Propagation
 Ionosphere
Propagation
 Ionosphere
 E-Layer Propagation
 Sporadic-E
 Can occur any time during the solar cycle
 Highest probability: Early summer and mid-winter
 HF Bands: 10 meters, 6 meters, and 2 meters
 Aurora (Northern latitudes)
 Rapid signal strength changes
 Sounds fluttery or distorted
 Primarily on 6 meters
 Meteor scatter
 Primarily 6 meters
Propagation
 Ionosphere
 The lowers regions of the ionosphere absorb
radio waves
 Primarily D-layer
 Some absorption in E-layer
 The longer the wavelength (lower frequency), the
more absorption
 Little to no communications possible on lower
frequency bands during the day when D and E layer
are present
T3A11 -- Which part of the atmosphere enables
the propagation of radio signals around the
world?
A. The stratosphere
B. The troposphere
C. The ionosphere
D. The magnetosphere
T3C01 -- Why are direct (not via a repeater) UHF
signals rarely heard from stations outside your
local coverage area?
A. They are too weak to go very far
B. FCC regulations prohibit them from going
more than 50 miles
C. UHF signals are usually not reflected by the
ionosphere
D. They collide with trees and shrubbery and
fade out
T3C02 -- Which of the following might be
happening when VHF signals are being received
from long distances?
A. Signals are being reflected from outer space
B. Signals are arriving by sub-surface ducting
C. Signals are being reflected by lightning
storms in your area
D. Signals are being refracted from a sporadic E
layer
T3C03 -- What is a characteristic of VHF signals
received via auroral reflection?
A. Signals from distances of 10,000 or
more miles are common
B. The signals exhibit rapid fluctuations of
strength and often sound distorted
C. These types of signals occur only during
winter nighttime hours
D. These types of signals are generally
strongest when your antenna is aimed
west
T3C04 -- Which of the following propagation types
is most commonly associated with occasional
strong over-the-horizon signals on the 10, 6, and 2
meter bands?
A.
B.
C.
D.
Backscatter
Sporadic E
D layer absorption
Gray-line propagation
T3C07 -- What band is best suited for
communicating via meteor scatter?
A. 10 meters
B. 6 meters
C. 2 meters
D. 70 cm
T3C09 -- What is generally the best time for
long-distance 10 meter band propagation via
the F layer?
A. From dawn to shortly after sunset during
periods of high sunspot activity
B. From shortly after sunset to dawn during
periods of high sunspot activity
C. From dawn to shortly after sunset during
periods of low sunspot activity
D. From shortly after sunset to dawn during
periods of low sunspot activity
T3C12 -- Which of the following bands may
provide long distance communications during
the peak of the sunspot cycle?
A. Six or ten meters
B. 23 centimeters
C. 70 centimeters or 1.25 meters
D. All of these choices are correct
Antenna Fundamentals
 Definitions:
 Antenna: Converts an RF electrical signal into an
electromagnetic wave (radio wave) or vice versa
 Any electrical conductor can act as an antenna
 Some sizes and configurations work better than others
 Feed-line: Conducts the RF electrical signal
to/from the antenna
 a.k.a. Transmission line
Antenna Fundamentals
 Definitions:
 Feed Point: Place where the feed-line is
connected to the antenna
 Feed Point Impedance: Ratio of RF voltage to
RF current at the feed point
 If impedance is purely resistive (no reactance) then
antenna is said to be “resonant”
Antenna Fundamentals
 Definitions:
 Antenna Elements: Conductive parts of an
antenna
 Driven Element: Element that feed-line is connected
to
 Driven Array: More than one driven element
 Parasitic Element(s): Element(s) not directly
connected to feed-line
 Reflector
 Director
Antenna Fundamentals
 Polarization
 An electromagnetic wave consists of an electric
wave and magnetic wave that propagate at right
angles to each other
 Polarization is the orientation of the electric wave
with respect to the earth
Antenna Fundamentals
 Polarization
 If the electric wave is horizontal (parallel to the
ground), then wave is said to be horizontally
polarized
 If electric wave is vertical (perpendicular to the
ground), then wave is said to be vertically
polarized
Antenna Fundamentals
 Polarization
Antenna Fundamentals
 Polarization
 The direction of the electric field is the same as
the orientation of the antenna element
 Loop antennas and circular polarization are exceptions
 At VHF and UHF frequencies, if polarizations of
transmit and receive antenna do not match,
reduced received signal strength results
 Polarization of refracted sky wave signals is
random and continuously changing
 Elliptically polarized
 An antenna of any orientation may be used
T3A04 -- What can happen if the antennas at
opposite ends of a VHF or UHF line of sight radio
link are not using the same polarization?
A. The modulation sidebands might become
inverted
B. Signals could be significantly weaker
C. Signals have an echo effect on voices
D. Nothing significant will happen
T3A07 -- What type of wave carries radio signals
between transmitting and receiving stations?
A. Electromagnetic
B. Electrostatic
C. Surface acoustic
D. Magnetostrictive
T3A09 -- Which of the following results from the
fact that skip signals refracted from the
ionosphere are elliptically polarized?
A. Digital modes are unusable
B. Either vertically or horizontally polarized
antennas may be used for transmission or
reception
C. FM voice is unusable
D. Both the transmitting and receiving antennas
must be of the same polarization
T3B02 -- What property of a radio wave is used
to describe its polarization?
A. The orientation of the electric field
B. The orientation of the magnetic field
C. The ratio of the energy in the magnetic field
to the energy in the electric field
D. The ratio of the velocity to the wavelength
T3B03 -- What are the two components of a
radio wave?
A. AC and DC
B. Voltage and current
C. Electric and magnetic fields
D. Ionizing and non-ionizing radiation
T5C07 -- What is a usual name for
electromagnetic waves that travel through
space?
A.
B.
C.
D.
Gravity waves
Sound waves
Radio waves
Pressure waves
T9A02 -- Which of the following is true
regarding vertical antennas?
A. The magnetic field is perpendicular to the
Earth
B. The electric field is perpendicular to the
Earth
C. The phase is inverted
D. The phase is reversed
Antenna Fundamentals
 Decibels
 The difference in strength between 2 signals is
often expressed in decibels (dB)
 Ratio between 2 values… a comparison
 Based on logarithmic scale
Antenna Fundamentals
 Decibels
 Commonly used to:
 Specify gain of an amplifier
 Specify gain of an antenna
 Specify loss in a feed line
 Comparing output vs input level
Antenna Fundamentals
 Decibels
 Ratio between 2 values
 One value is often a standard reference value, e.g.,
1 watt or 1 milliwatt
 Logarithmic scale
 Power ratio:
dB = 10 log10(P1/P2)
 Voltage ratio:
dB = 20 log10(P1/P2)
 Where P1 is output and P2 is input
 If dB is positive => gain
 If dB is negative => loss
Antenna Fundamentals
dB
Ratio
dB
Ratio
0
1.000
0
1.000
-1
0.794
1
1.259
-2
0.631
2
1.585
-3
0.501
3
1.995
-4
0.398
4
2.512
-5
0.316
5
3.162
-6
0.250
6
4.000
-7
0.200
7
5.012
-8
0.159
8
6.310
-9
0.126
9
7.943
-10
0.100
10
10.00
T5B09 -- What is the approximate amount of
change, measured in decibels (dB), of a power
increase from 5 watts to 10 watts?
A. 2 dB
B. 3 dB
C. 5 dB
D. 10 dB
T5B10 -- What is the approximate amount of
change, measured in decibels (dB), of a power
decrease from 12 watts to 3 watts?
A. -1 dB
B. -3 dB
C. -6 dB
D. -9 dB
T5B11 -- What is the approximate amount of
change, measured in decibels (dB), of a power
increase from 20 watts to 200 watts?
A. 10 dB
B. 12 dB
C. 18 dB
D. 28 dB
Antenna Fundamentals
 Antenna Gain
 Omni-directional antennas radiate equally in all
directions
 Directional antennas focus radiation in one or
more specific directions, e.g., beam antennas
 Gain is the apparent increase in power in a
particular direction because energy is focused in
that direction
 Measured in decibels (dB)
Antenna Fundamentals
 Radiation Patterns
 A way of visualizing
antenna performance
 The further the line is
away from the center of
the graph, the stronger
the signal in that
direction (gain)
Antenna Fundamentals
 Radiation Patterns
T9A11 -- What is meant by the gain of an
antenna?
A. The additional power that is added to the
transmitter power
B. The additional power that is lost in the
antenna when transmitting on a higher
frequency
C. The increase in signal strength in a
specified direction when compared to a
reference antenna
D. The increase in impedance on receive or
transmit compared to a reference antenna
Feed Lines and SWR
 Feed Lines
 Feed lines are used for:
 Conducting RF voltage between radio and antenna
 Connecting RF voltage between pieces of equipment
 Feed lines are constructed using special materials
and configurations. Objectives:
 Maintain constant impedance
 Minimize losses
 SWR: Standing Wave Ratio
Feed Lines and SWR
 Feed Lines
 Coaxial cable
 Usually shortened to “coax”
 Most popular type
 Easy to work with
 Low characteristic impedance
 Typically 50Ω or 75Ω
 Moderate to high loss
 Loss varies with frequency
 Higher frequency  higher loss
Feed Lines and SWR
 Feed Lines
 Coaxial cable
 Characteristic impedance primarily determined by
ratio of diameter of shield to diameter of center
conductor
 Larger ratio  higher impedance


50Ω = RG-8, RG-8X, RG-58, RG-174
75Ω = RG-6, RG-11, RG-59
Feed Lines and SWR
 Feed Lines
 Coaxial cable
 Energy lost in feed line is converted to heat
 Loss is primarily determined by size of cable and by
the cable’s insulating material
 Larger diameter  Lower loss
 Air is lowest loss insulator
 Foam dielectric coax has lower loss than solid
dielectric coax because it has more air
 Air-insulated hard line
Feed Lines and SWR
 Feed Lines
 Parallel-wire transmission line
 Open-wire line, window line, twin lead
 More difficult to work with
 High characteristic impedance
 Typically 300Ω to 600Ω
 Very low loss
Feed Lines and SWR
 Characteristic Impedance
 Every transmission line has a characteristic
impedance
 Denoted as Z0
 Measure of how RF energy flows down the line
 Determined by the physical dimensions of cable
 NOT the same as the ohmic resistance of the
conductors that make up the line
Feed Lines and SWR
 Characteristic Impedance
 Parallel-wire transmission line
 Characteristic impedance determined by ratio of
diameter of conductors to distance between them
 Larger distance  higher impedance
 Smaller diameter conductors  higher impedance
T7C07 -- What happens to power lost in a feed
line?
A. It increases the SWR
B. It comes back into your transmitter and
could cause damage
C. It is converted into heat
D. It can cause distortion of your signal
T7C12 -- Which of the following is a common
use of coaxial cable?
A. Carrying dc power from a vehicle battery to
a mobile radio
B. Carrying RF signals between a radio and
antenna
C. Securing masts, tubing, and other cylindrical
objects on towers
D. Connecting data signals from a TNC to a
computer
T9B02 -- What is the impedance of the most
commonly used coaxial cable in typical
amateur radio installations?
A. 8 ohms
B. 50 ohms
C. 600 ohms
D. 12 ohms
T9B03 -- Why is coaxial cable used more often
than any other feed line for amateur radio
antenna systems?
A. It is easy to use and requires few special
installation considerations
B. It has less loss than any other type of feed
line
C. It can handle more power than any other
type of feed line
D. It is less expensive than any other types of
feed line
T9B05 -- What generally happens as the
frequency of a signal passing through coaxial
cable is increased?
A. The apparent SWR increases
B. The reflected power increases
C. The characteristic impedance increases
D. The loss increases
T9B11 -- Which of the following types of feed
line has the lowest loss at VHF and UHF?
A. 50-ohm flexible coax
B. Multi-conductor unbalanced cable
C. Air-insulated hard line
D. 75-ohm flexible coax
Break
Feed Lines and SWR
 Standing Wave Ratio (SWR)
 If feed line impedance = antenna impedance,
then:
 All energy is delivered to the antenna
 Perfect match
 SWR = 1:1
 If feed line impedance ≠ antenna impedance,
then:
 Some energy is reflected back towards the source
 Reflected energy is often lost as heat
 SWR = ZLine / ZAnt or SWR = ZAnt / Zline
 Ratios are always greater than 1:1, e.g., 1.3:1, 2:1, 3:1
Feed Lines and SWR
 Standing Wave Ratio (SWR)
 Rule-of-thumb guidelines:
 1:1 = Perfect
 2:1 = Acceptable
 Modern transmitters will automatically reduce transmitter
output power when SWR is above 2:1
 2:1 to 3:1= Useable (with tuner)
 Many transceivers have an internal antenna tuner which will
match SWRs up to 3:1
 3:1 or more = Really bad
T7C03 -- What, in general terms, is standing
wave ratio (SWR)?
A. A measure of how well a load is matched to
a transmission line
B. The ratio of high to low impedance in a feed
line
C. The transmitter efficiency ratio
D. An indication of the quality of your station’s
ground connection
T7C04 -- What reading on an SWR meter
indicates a perfect impedance match between
the antenna and the feed line?
A. 2 to 1
B. 1 to 3
C. 1 to 1
D. 10 to 1
T7C05 -- What is the approximate SWR value
above which the protection circuits in most
solid-state transmitters begin to reduce
transmitter power?
A. 2 to 1
B. 1 to 2
C. 6 to 1
D. 10 to 1
T7C06 -- What does an SWR reading of 4:1
indicate?
A. Loss of -4dB
B. Good impedance match
C. Gain of +4dB
D. Impedance mismatch
T9B01 -- Why is it important to have a low
SWR in an antenna system that uses coaxial
cable feed line?
A. To reduce television interference
B. To allow the efficient transfer of power
and reduce losses
C. To prolong antenna life
D. All of these choices are correct
T9B09 -- What might cause erratic changes in
SWR readings?
A. The transmitter is being modulated
B. A loose connection in an antenna or a feed
line
C. The transmitter is being over-modulated
D. Interference from other stations is
distorting your signal
Practical Antenna Systems
 Dipoles and Ground Planes
 Dipole (Horizontal)





Most basic antenna
Two conductors, equal length
Feed line connected in the middle
Total length is 1/2 wavelength (1/2 λ)
Length (feet) = 468 / Frequency (MHz)
Practical Antenna Systems
 Dipoles and Ground Planes
 Dipole antenna construction
Practical Antenna Systems
 Dipoles and Ground Planes
 Typical dipole antenna installations
Practical Antenna Systems
 Dipoles and Ground Planes
 Dipole radiation pattern (azimuthal)
Practical Antenna Systems
 Dipoles and Ground Planes
 Dipole (Vertical)
 One half of a dipole oriented perpendicular to
the Earth’s surface
 Other half of the dipole is replaced by a ground
plane, e.g., Earth, car roof, trunk lid, or other
metal surface
 When “Earth mounted”, radial wires required
 Omni-directional
 Length (feet) = 234 / Frequency (MHz)
Practical Antenna Systems
 Dipoles and Ground Planes
 Vertical antennas dimensions
Practical Antenna Systems
 Dipoles and Ground Planes
 Vertical antenna installation
Practical Antenna Systems
 Dipoles and Ground Planes
 Mobile antennas
 Most mobile antennas are a variation of the vertical
(ground plane) antenna
 If antenna cannot be a full 1/4λ long, an inductor
(coil) is added to make antenna electrically longer
 Mounting antenna in center of roof gives most
uniform radiation pattern
Practical Antenna Systems
 Dipoles and Ground Planes
 Mobile antennas
 A popular mobile antenna for VHF & UHF is the 5/8λ
vertical
 Low angle of radiation (“low take-off angle”)
 Provides a gain of 1.5 dB over a 1/4λ vertical antenna
Practical Antenna Systems
 Dipoles and Ground Planes
 “Rubber Duck” Antennas
 Variation of the ground-plane
 Commonly used on hand-held transceivers
 Coil of wire enclosed in rubber (plastic) covering
 Shorter than normal ground-plane
 Much less efficient than full-sized ground-plane
Side note: Using a rubber duck antenna inside your vehicle is
ineffective and not a good idea because….
Signals transmitted outside the vehicle are weaker due to the
shielding provided by the vehicle’s body
Practical Antenna Systems
 Loop Antennas
 Loop of wire
 Circumference is one wavelength (1λ) long
 Circular, triangular (delta), or square (quad)
configurations
 Oriented vertically or horizontally
 If oriented vertically, can be either vertically or
horizontally polarized
T9A03 -- Which of the following describes a
simple dipole mounted so the conductor is
parallel to the Earth's surface?
A. A ground wave antenna
B. A horizontally polarized antenna
C. A rhombic antenna
D. A vertically polarized antenna
T9A04 -- What is a disadvantage of the “rubber
duck” antenna supplied with most handheld
radio transceivers?
A. It does not transmit or receive as
effectively as a full-sized antenna
B. It transmits a circularly polarized signal
C. If the rubber end cap is lost it will unravel
very quickly
D. All of these choices are correct
T9A05 -- How would you change a dipole
antenna to make it resonant on a higher
frequency?
A.
B.
C.
D.
Lengthen it
Insert coils in series with radiating wires
Shorten it
Add capacitive loading to the ends of the
radiating wires
T9A07 -- What is a good reason not to use a
“rubber duck” antenna inside your car?
A. Signals can be significantly weaker than
when it is outside of the vehicle
B. It might cause your radio to overheat
C. The SWR might decrease, decreasing the
signal strength
D. All of these choices are correct
T9A08 -- What is the approximate length, in
inches, of a quarter-wavelength vertical
antenna for 146 MHz?
A. 112
B. 50
C. 19
D. 12
T9A09 -- What is the approximate length, in
inches, of a 6 meter 1/2-wavelength wire
dipole antenna?
A. 6
B. 50
C. 112
D. 236
T9A10 -- In which direction is the radiation
strongest from a half-wave dipole antenna in
free space?
A. Equally in all directions
B. Off the ends of the antenna
C. Broadside to the antenna
D. In the direction of the feed line
T9A12 -- What is a reason to use a properly
mounted 5/8 wavelength antenna for VHF or
UHF mobile service?
A. It offers a lower angle of radiation and more gain
than a 1/4 wavelength antenna and usually provides
improved coverage
B. It features a very high angle of radiation and is
better for communicating via a repeater
C. The 5/8 wavelength antenna completely eliminates
distortion caused by reflected signals
D. The 5/8 wavelength antenna offers a 10-times
power gain over a 1/4 wavelength design
T9A13 -- Why are VHF or UHF mobile antennas
often mounted in the center of the vehicle
roof?
A. Roof mounts have the lowest possible SWR
of any mounting configuration
B. Only roof mounting can guarantee a
vertically polarized signal
C. A roof mounted antenna normally provides
the most uniform radiation pattern
D. Roof mounted antennas are always the
easiest to install
T9A14 -- Which of the following terms
describes a type of loading when referring to
an antenna?
A. Inserting an inductor in the radiating portion of
the antenna to make it electrically longer
B. Inserting a resistor in the radiating portion of the
antenna to make it resonant
C. Installing a spring at the base of the antenna to
absorb the effects of collisions with other objects
D. Making the antenna heavier so it will resist wind
effects when in motion
Practical Antenna Systems
 Directional antennas
 Directional antennas focus or direct RF energy in
a given direction
 Gain
 Apparent increase in power in the desired direction
(both transmit and receive)
Practical Antenna Systems
 Directional antennas
 The most common type of directional antenna is
the beam
 The most common type of beam antennas is:
 Yagi-Uda array
 Normally just called a “Yagi”
 Invented in 1926 by Dr. Shintaro Uda, in
collaboration with Dr. Hidetsugu Yagi
Practical Antenna Systems
 Directional antennas
 All beam antennas are made up of elements
 Metal rods
 Loops of wire
 Driven element is connected to the radio by the
feed line
 Reflector element is on the side opposite the
desired radiation direction
 Director element is on the side toward the
desired direction
 Can have more then one director
Practical Antenna Systems
 Directional antennas
 Yagi antenna
 Horizontally-polarized Yagi antenna is commonly
used for long distance, weak signal CW & SSB
communications on VHF & UHF
Practical Antenna Systems
 Directional antennas
 Quad antenna
 Square wire loop elements
Practical Antenna Systems
 Directional Antennas
 Parabolic Dish
 Large, round, curved
reflector
 Very high gain
T3A03 -- What antenna polarization is normally
used for long-distance weak-signal CW and SSB
contacts using the VHF and UHF bands?
A. Right-hand circular
B. Left-hand circular
C. Horizontal
D. Vertical
T3A05 -- When using a directional antenna,
how might your station be able to access a
distant repeater if buildings or obstructions are
blocking the direct line of sight path?
A. Change from vertical to horizontal
polarization
B. Try to find a path that reflects signals to
the repeater
C. Try the long path
D. Increase the antenna SWR
T9A01 -- What is a beam antenna?
A. An antenna built from aluminum I-beams
B. An omnidirectional antenna invented by
Clarence Beam
C. An antenna that concentrates signals in
one direction
D. An antenna that reverses the phase of
received signals
T9A06 -- What type of antennas are the quad,
Yagi, and dish?
A. Non-resonant antennas
B. Loop antennas
C. Directional antennas
D. Isotropic antennas
Practical Antenna Systems
 Practical feed lines and associated
equipment
 Feed line selection and maintenance
 Coax vs. Open Wire
 Coax is easier to use
 VHF & UHF installations almost always use
coaxial cable
 Open wire has lower loss
 Normally used only with HF wire antennas
Practical Antenna Systems
 Practical feed lines and associated equipment
 Feed line selection and maintenance
 Need to consider:




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Frequency
Length of cable
Power level
Budget
Loss
Larger cable generally has lower loss
Foam dielectric cable has lower loss
Practical Antenna Systems
Type
Impedance
Loss @ 30MHz
Loss @ 150MHz
Cost
(dB/100ft)
(dB/100ft)
(per foot)
RG-174
50Ω
4.6 dB
10.3 dB
$0.20
RG-58
50Ω
2.5 dB
5.6 dB
$0.28
RG-8X
50Ω
2.0 dB
4.5 dB
$0.30
RG-8
50Ω
1.1 dB
2.5 dB
$1.00
RG-213
50Ω
1.1 dB
2.5 dB
$0.89
LMR-400
50Ω
0.7 dB
1.5 dB
$1.11
Type
Impedance
Loss @ 30MHz
Loss @ 150MHz
Cost
(dB/100ft)
(dB/100ft)
(per foot)
RG-59
75Ω
1.8 dB
4.1 dB
$0.16
RG-6
75Ω
1.4 dB
3.3 dB
$0.24
RG-11A
75Ω
0.7 dB
1.6 dB
$0.97
Practical Antenna Systems
 Practical feed lines and associated equipment
 Feed line selection and maintenance
 Coaxial cable must be protected




Worst enemy is moisture getting into the cable
Moisture increases loss in cable
Avoid nicks or cuts in outer jacket
Prolonged exposure to sunlight can result in tiny cracks in
outer jacket which can admit moisture
 Seal outside connections against moisture
 Avoid sharp bends or turns
Practical Antenna Systems
 Practical feed lines and associated
equipment
 Coaxial feed line connections
 4 main types commonly used in amateur radio:




UHF
Type “N”
BNC
SMA
Practical Antenna Systems
 Practical feed lines and associated equipment
 Coaxial feed line connections
 UHF connectors








Most common type
Up to 150 MHz
High power (>1.5 kW)
Not constant impedance
Not weather resistant
Inexpensive
Plug = PL-259 (male)
Socket = SO-239 (female)
Practical Antenna Systems
 Practical feed lines and associated equipment
 Coaxial feed line connections
 Type “N” connectors







Up to 10 GHz
High power (>1.5 kW)
Constant impedance
Both 50Ω and 75Ω versions
Weather resistant
Relatively expensive
Relatively difficult to install
Practical Antenna Systems
 Practical feed lines and associated equipment
 Coaxial feed line connections
 BNC Connectors





Up to 4 GHz
Low power
Constant impedance
Both 50Ω and 75Ω versions
Commonly used on:
 Older hand held radios
 Test equipment
Practical Antenna Systems
 Practical feed lines and associated
equipment
 Coaxial feed line connections
 SMA connectors





Up to 18 GHz
Low power
Constant impedance
Only 50Ω available
Used on most new hand held radios
T7C09 -- Which of the following is the most
common cause for failure of coaxial cables?
A. Moisture contamination
B. Gamma rays
C. The velocity factor exceeds 1.0
D. Overloading
T7C10 -- Why should the outer jacket of coaxial
cable be resistant to ultraviolet light?
A. Ultraviolet resistant jackets prevent
harmonic radiation
B. Ultraviolet light can increase losses in the
cable’s jacket
C. Ultraviolet and RF signals can mix together,
causing interference
D. Ultraviolet light can damage the jacket and
allow water to enter the cable
T7C11 -- What is a disadvantage of air core
coaxial cable when compared to foam or solid
dielectric types?
A. It has more loss per foot
B. It cannot be used for VHF or UHF antennas
C. It requires special techniques to prevent
water absorption
D. It cannot be used at below freezing
temperatures
Practical Antenna Systems
 Soldering
 A process in which two or more metal items are
joined together by melting and flowing a filler
metal into the joint
 The filler metal is called solder
 Flux is a material used to prevent the formation
of oxides during the soldering process
Practical Antenna Systems
 Soldering
 Types of solder
 Standard solder is a mixture of tin and lead
 Ratio of tin to lead is adjusted for lowest melting
temperature
 63/37 or 60/40
 Melting point is about 183°C (361°F)
 Lead-free solder is a mixture of tin & silver
or tin, silver, and copper
 Melting point is about 40°C (72°F) hotter than
standard solder
Practical Antenna Systems
 Soldering
 Types of flux
 Resin
 Used for electrical/electronic connections
 Acid
 Used for plumbing
NEVER use acid–core solder or acid
flux to solder electronic connections!
Practical Antenna Systems
 Soldering
 It takes a little bit of
skill to make a good
solder joint
 Good solder joint is
bright & shiny
 If joint is not heated
enough or if it is
moved before it
cools, it can result in
a “cold solder joint”
 Cold solder joint is
dull & grainy-looking
T7D08 -- Which of the following types of solder
is best for radio and electronic use?
A. Acid-core solder
B. Silver solder
C. Rosin-core solder
D. Aluminum solder
T7D09 -- What is the characteristic appearance of
a cold solder joint?
A. Dark black spots
B. A bright or shiny surface
C. A grainy or dull surface
D. A greenish tint
Practical Antenna Systems
 Practical feed lines and associated
equipment
 SWR meters and Wattmeters
 SWR meter
 a.k.a. SWR bridge
 Connects between transmitter and feed line
 Displays amount of mismatch (SWR) between transmitter
and antenna system

Antenna system = antenna + feed line
 Make adjustments to antenna system to minimize
mismatch
Practical Antenna Systems
 Practical feed lines and associated equipment
 SWR meters and Wattmeters
 SWR meter location
Practical Antenna Systems
 Practical feed lines and
associated equipment
 SWR meters and
Wattmeters
 Simple SWR meter
 Set to “FWD”
 Adjust “CAL” for full
scale reading
 Set to “REF” and read
SWR
Practical Antenna Systems
 Practical feed lines
and associated
equipment
 SWR Meters and
Wattmeters
 Cross-needle SWR
meter
 No adjustments
necessary
Practical Antenna Systems
 Practical feed lines and
associated equipment
 SWR Meters and
Wattmeters
 Directional Wattmeter
 Measures both forward power
(PF) & reflected power (PR)
 SWR can then be calculated
from PF & PR
Practical Antenna Systems
 Practical feed lines and associated
equipment
 Antenna tuner




Used to make antenna matching adjustments
Tuners are impedance transformers
When used appropriately they are effective
When used inappropriately all they do is make a
bad antenna look good to the transmitter…the
antenna is still bad
Practical Antenna Systems
 Practical feed lines and associated equipment
 Antenna tuner
 a.k.a. Transmatch
 Does NOT “tune” the antenna
 Makes transmitter think all impedances are matched
Practical Antenna Systems
 Practical feed lines and associated equipment
 Antenna analyzer
 Measures antenna impedance (Z)
 Resistance (R)
 Reactance (X)
 Several other useful functions
Practical Antenna Systems
 Practical feed lines and associated equipment
 Dummy load
 A non-radiating load used for testing
 Typically 50Ω
T4A05 -- Where should an in-line SWR meter be
connected to monitor the standing wave ratio
of the station antenna system?
A. In series with the feed line, between the
transmitter and antenna
B. In series with the station's ground
C. In parallel with the push-to-talk line and the
antenna
D. In series with the power supply cable, as
close as possible to the radio
T7C02 -- Which of the following instruments can
be used to determine if an antenna is resonant
at the desired operating frequency?
A. A VTVM
B. An antenna analyzer
C. A Q meter
D. A frequency counter
T7C08 -- What instrument other than an SWR
meter could you use to determine if a feed line
and antenna are properly matched?
A. Voltmeter
B. Ohmmeter
C. Iambic pentameter
D. Directional wattmeter
Questions?